The loading of unmanned barges is not regulated in Canada. The amount of cargo carried by any such barge between Canadian ports or between Canadian and United States ports within the treaty zone on the west coast is thus established by practice. The draught survey data showed that the barge was carrying a weight of approximately 193 short tons (175 tonnes), of an unknown origin, before the loading of the iron scrap began. It is unlikely that the light ship weight of the barge would increase by this quantity after the deadweight scale was compiled in 1976. The barge did not undergo any modification and no permanent structures were added to the hull or to the cargo box. Therefore, the only conceivable explanation of this initial load is the presence of water in underdeck compartments. The damaged shell plating obviously allowed for a slow ingress of water into the compartment No.4 during previous voyages of the loaded barge. A possible scenario leading to the capsizing may be deduced based on the known facts. As soon as the fracture became submerged during the loading of the scrap onto the barge in Victoria, more water was able to flow into the compartment. Consequently, the air pressure in the compartment would have built up, retarding the ingress of water. However, the air might leak out slowly through deck fittings such as manholes and sounding plugs. Thus, the slow ingress of water would have continued. The loaders, unaware of the water flowing into the hull, corrected the trim and list by simply stowing the cargo accordingly. During the voyage, the water would have flowed into the same starboard side compartment until there was enough weight to cause the deck edge to submerge and the barge's righting moment to decrease. The list would then increase until the cargo started shifting to one side. The combined weight of the water and the shifted cargo probably caused the barge to capsize. The weather conditions during the voyage induced a rolling of the barge and added some water to the deck cargo. These additional, external factors certainly hastened the capsizing.Analysis The loading of unmanned barges is not regulated in Canada. The amount of cargo carried by any such barge between Canadian ports or between Canadian and United States ports within the treaty zone on the west coast is thus established by practice. The draught survey data showed that the barge was carrying a weight of approximately 193 short tons (175 tonnes), of an unknown origin, before the loading of the iron scrap began. It is unlikely that the light ship weight of the barge would increase by this quantity after the deadweight scale was compiled in 1976. The barge did not undergo any modification and no permanent structures were added to the hull or to the cargo box. Therefore, the only conceivable explanation of this initial load is the presence of water in underdeck compartments. The damaged shell plating obviously allowed for a slow ingress of water into the compartment No.4 during previous voyages of the loaded barge. A possible scenario leading to the capsizing may be deduced based on the known facts. As soon as the fracture became submerged during the loading of the scrap onto the barge in Victoria, more water was able to flow into the compartment. Consequently, the air pressure in the compartment would have built up, retarding the ingress of water. However, the air might leak out slowly through deck fittings such as manholes and sounding plugs. Thus, the slow ingress of water would have continued. The loaders, unaware of the water flowing into the hull, corrected the trim and list by simply stowing the cargo accordingly. During the voyage, the water would have flowed into the same starboard side compartment until there was enough weight to cause the deck edge to submerge and the barge's righting moment to decrease. The list would then increase until the cargo started shifting to one side. The combined weight of the water and the shifted cargo probably caused the barge to capsize. The weather conditions during the voyage induced a rolling of the barge and added some water to the deck cargo. These additional, external factors certainly hastened the capsizing. The unmanned barge SEASPAN177 capsized while under tow. Damage to the barge's side shell plating allowed for the ingress of water into the underdeck void space. The barge did not have a designated load line establishing safe maximum load and minimum freeboard. The cargo slid off the barge's deck and was lost.Findings The unmanned barge SEASPAN177 capsized while under tow. Damage to the barge's side shell plating allowed for the ingress of water into the underdeck void space. The barge did not have a designated load line establishing safe maximum load and minimum freeboard. The cargo slid off the barge's deck and was lost. The SEASPAN177 capsized because the hull damage allowed for the ingress of sea water into two underdeck compartments. This ingress created a heeling moment and caused the barge to lose its transverse stability. The cause of the hole in the starboard side of the barge's shell plating was not determined.Causes and Contributing Factors The SEASPAN177 capsized because the hull damage allowed for the ingress of sea water into two underdeck compartments. This ingress created a heeling moment and caused the barge to lose its transverse stability. The cause of the hole in the starboard side of the barge's shell plating was not determined.